drm/exynos: Init the DSIM PHY in samsung_dsim_enable()

In case the PHY is not initialized, do it in samsung_dsim_enable(),
otherwise the link configuration registers are not programmed at all.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Guido Günther <agx@sigxcpu.org>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Michael Tretter <m.tretter@pengutronix.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
To: dri-devel@lists.freedesktop.org